You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

**alvinero****Member**- Registered: 2017-07-31
- Posts: 1

Hello, a friend of mine suggested me this problem:

Find a number n that, when you swap the first and last digits, it becomes 2n. Please, try to find it in decimal system.

Offline

Hi alvinero,

Welcome to the forum. Any restrictions on the number of digits? For instance, n = 0 works. Two digits can be ruled out by letting n = 10a + b (which has no solutions as per your constraints), and three digits can also be ruled out the same way via modulo arithmetic. If a non-trivial solution exists, it may be large.

EDIT: I have a solution, but it is 21 digits long. I don't know if this is the smallest such solution (and, if this was intended to be a quick brain teaser, it seems unlikely to be). I'll post up a rough solution tomorrow.

**LearnMathsFree: Videos on various topics.New: Integration Problem | Adding FractionsPopular: Continued Fractions | Metric Spaces | Duality**

Offline

Apparently the smallest number has 18 digits.

https://www.youtube.com/watch?v=1lHDCAIsyb8

https://mindyourdecisions.com/blog/2017 … ay-puzzle/

**230** books currently added on Goodreads

Offline

Thanks for the solution, it is an interesting problem.

**LearnMathsFree: Videos on various topics.New: Integration Problem | Adding FractionsPopular: Continued Fractions | Metric Spaces | Duality**

Offline

Pages: **1**